crc8: Use explicit error type

CHANGELOG.md

@@ -4,6 +4,12 @@ This project follows [semantic versioning](https://semver.org/).
 
 ## [Unreleased]
 
+### Changed
+
+ * Add a separate error type for the crc8 module to allow for
+   `From<crc8::Error>` implementations.
+   ([#18](https://github.com/Sensirion/sensirion-i2c-rs/pull/18/))
+
 ## [0.1.1] (2020-09-02)
 
 ### Changed

src/crc8.rs

@@ -1,5 +1,12 @@
 //! Helper functions for CRC8 checksum validation
 
+/// Errors which can happen in the crc8 module
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Error {
+    /// CRC validation failed
+    CrcError,
+}
+
 /// Calculate the CRC8 checksum.
 pub fn calculate(data: &[u8]) -> u8 {
     const CRC8_POLYNOMIAL: u8 = 0x31;
@@ -27,11 +34,11 @@ pub fn calculate(data: &[u8]) -> u8 {
 ///
 /// This method will consider every third byte a checksum byte. If the buffer size is not a
 /// multiple of 3, then it will panic.
-pub fn validate(buf: &[u8]) -> Result<(), ()> {
+pub fn validate(buf: &[u8]) -> Result<(), Error> {
     assert!(buf.len() % 3 == 0, "Buffer must be a multiple of 3");
     for chunk in buf.chunks(3) {
         if calculate(&[chunk[0], chunk[1]]) != chunk[2] {
-            return Err(());
+            return Err(Error::CrcError);
         }
     }
     Ok(())
@@ -66,6 +73,9 @@ mod tests {
         crc8::validate(&[0xbe, 0xef, 0x92]).unwrap();
 
         // Invalid CRC
-        assert_eq!(crc8::validate(&[0xbe, 0xef, 0x91]), Err(()));
+        assert_eq!(
+            crc8::validate(&[0xbe, 0xef, 0x91]),
+            Err(crc8::Error::CrcError)
+        );
     }
 }

src/i2c.rs

@@ -11,6 +11,14 @@ pub enum Error<I2cWrite: i2c::Write, I2cRead: i2c::Read> {
     Crc,
 }
 
+impl<W: i2c::Write, R: i2c::Read> From<crc8::Error> for Error<W, R> {
+    fn from(err: crc8::Error) -> Error<W, R> {
+        match err {
+            crc8::Error::CrcError => Error::Crc,
+        }
+    }
+}
+
 /// Write an u16 command to the I²C bus.
 pub fn write_command<I2cWrite: i2c::Write>(
     i2c: &mut I2cWrite,
@@ -38,7 +46,8 @@ pub fn read_words_with_crc<I2c: i2c::Read + i2c::Write>(
         "Buffer must hold a multiple of 3 bytes"
     );
     i2c.read(addr, data).map_err(Error::I2cRead)?;
-    crc8::validate(data).map_err(|_| Error::Crc)
+    crc8::validate(data)?;
+    Ok(())
 }
 
 #[cfg(test)]